The present invention relates to information storage systems and in particular to electromagnetic transducers for hard disk drives.
Traditional electromagnetic transducers employ a magnetically permeable core coupled with a conductive coil in order to write and read data in an associated magnetic recording surface. In a hard disk drive, such transducers are usually spaced from the rapidly spinning rigid disk by a thin layer of air that moves with the disk surface, often termed an air bearing. This spacing is believed to be important in avoiding damage between the rapidly spinning disk and the transducer, which is appended to a substrate designed to xe2x80x9cflyxe2x80x9d slightly above the disk surface, buoyed by the moving air layer. This spacing or fly height, however, limits the density with which data can be stored and lowers the resolution and amplitude with which data can be retrieved. In recent years, durable sliding contact operation has been achieved which removes the air layer spacing and thereby enhances resolution, as disclosed in commonly assigned U.S. Pat. No. 5,041,932 to Hamilton.
Writing is typically performed by applying a current to the coil so that a magnetic field is induced in the adjacent magnetically permeable core, with the core transmitting a magnetic signal across any spacing and protective coating of the disk to magnetize a tiny pattern, or bit, of the media layer within the disk. Reading of information in the disk is performed by sensing the change in magnetic field of the core as the transducer passes over the bits in the disk, the changing magnetic field inducing a voltage or current in the inductively coupled coil. Alternatively, reading of the information may be accomplished by the employment of a magnetoresistive (MR) sensor, which has a resistance that varies as a function of the magnetic field adjacent to the sensor. In order to increase the amplitude and resolution in reading the bits, the MR sensor is typically positioned on the slider as close to the disk as possible.
Such a conventional MR sensor is formed of a very thin film with an edge facing and designed to be aligned with the recorded bits, and is subject to deleterious influences other than the magnetic field of the nearby bits. During manufacture, for instance, minor imperfections in material purity or thickness of the film can result in intolerable variations in magnetoresistance. Similarly, as little as ten millionths of an inch of wear of the sensor due to occasional contact with the disk is enough to cause most currently available, high-density MR hard disk drives to fail. Moreover, fluctuations in the temperature of the sensor can cause changes in resistance that may be confused with magnetic signals. In particular, even occasional contact between the transducer and the disk is known to result in such thermal fluctuations. Differing approaches have been used to avoid such thermal asperities. In U.S. Pat. No. 5,255,141, Valstyn et al. remove an MR or Hall effect sensor from the disk-facing surface of a flying head by utilizing a shunt that is switched to allow sufficient signals for both writing and reading. On the other hand, U.S. Pat. No. 5,455,730 to Dovek et al. employs a thick lubricant and a step to maintain separation between an MR sensor and the disk, and uses electronic manipulation to filter out magnetic signals from thermal noise.
An object of the present invention was to provide extremely high signal resolution in a hard disk drive system by designing a transducer to combine dynamic contact operation and MR sensing while keeping the wear and thermal noise from such contact from destroying the transducer or overwhelming the signal resolution.
The above object has been achieved in a hard disk drive system having a head in close proximity and therefore frequently if not continuously contacting the rapidly spinning rigid disk surface, the head employing a transducer with a magnetically permeable path between a poletip adjacent the disk surface and an MR sensor situated outside the range of thermal noise generated by the surface contact. The magnetically permeable path is the same as that used to write data to the disk, eliminating errors that occur in prior art transducers having MR sensors at a separate location from the writing poletips. Moreover, the magnetically permeable path is preferably formed in a low profile, highly efficient xe2x80x9cplanarxe2x80x9d loop that allows for manufacturing tolerances in throat height and wear of the terminal poletips from disk contact without poletip saturation or poletip smearing. Due to the high density and signal resolution afforded by such contact, sufficient signal is available for both writing and reading without the need for a shunt circuit.
In an ultralight, sliding contact embodiment, the transducer is formed primarily from a composite of thin-film layers with any bulk substrate removed. This transducer is designed to avoid flying and has such a low mass as to be insensitive to wear and shock. At least one disk-facing projection removes the vast majority of the transducer from the air that accompanies the spinning disk, reducing the lift felt by the transducer and allowing the projection to slide on the disk. In a somewhat larger partial or virtual contact embodiment, a substrate die remains attached to the thin-film layers on the side of the slider furthest from the disk, while the disk-facing layers are fashioned for an aerodynamic interaction with the moving air layer that causes the front of the slider to slightly raise while the rearward read/write poletips operate in virtual contact with the disk.
In either embodiment, the delicate MR layer is formed in one of the first manufacturing steps atop the substrate, so that the MR layer has a relatively uniform planar template that is free from contaminants. Forming the MR layer on such a flat, contaminate-free surface can dramatically increase the manufacturing yield. Also common to both the ultralight contact and the virtual contact embodiments is a low inductance, generally planar transducer that affords tolerance in throat height, both during manufacturing and later due to operational wear from contacting the disk. One embodiment of the planar transducer has a laminated yoke for improved high frequency efficiency, and the MR element in this case may be situated between the yoke lamina, which are also formed early in the process.
The shape of the MR layer is optimized for maximum efficiency and stability. Additional stability may be provided by exchange, permanent bias, end pinning or any other suitable. stabilization device. The preferred means for linearizing the MR output signal, in order to distinguish the orientations of recorded bits, is by flowing the electric current in the MR element in a direction between parallel and perpendicular to the magnetic flux from a signal. This canted current flow may be achieved by defining conductors adjoining the MR element, and a stabilization layer may optionally first be deposited on the MR element. Other linearizing and stabilizing schemes may employ a soft adjacent underlayer (SAL), permanent magnet layer, end pinning or other devices. The poletips are formed last, allowing for careful tailoring and last-minute variations in track width and other specifications.